1. Field of the Invention
The present invention relates to a backlight module, and more particularly, to an external electrode fluorescent lamp for use in a backlight module.
2. Descriptions of the Related Art
Because of making great progress in the manufacturing technology of the liquid crystal display (LCD), LCDs have many advantages such as light, thin, power-saving and radiation-less properties. Based on the above advantages, LCDs are widely used in various electrical products, for example, personal digital assistants (PDAs), notebook computers, digital cameras, digital camcorders, mobile telephones, computer monitors, and liquid crystal televisions. However, because the LCD panel cannot illuminate by itself, a backlight module is required to provide a light source for the LCD panel. The conventional backlight module has several cold cathode fluorescent lamps (CCFLs) as the light source to lighten the LCD panel.
A CCFL usually generates heat and hence leads to the nearby area at high temperature while emitting light. More particularly, as the required brightness of the LCD is gradually increasing, the increased brightness of the CCFL inevitably generates more heat, and the internal environmental temperature of the LCD is thus increased. Besides increase in heat, the driving voltage of the CCFLs also becomes higher. Consequently, the nearby environmental temperature of the CCFL would increase a lot, and thereby deteriorate the light emitting quality of the CCFL and the operating quality of the backlight module.
External electrode fluorescent lamps (EEFLs) are proposed to solve the problems mentioned above. FIG. 1 is a schematic diagram illustrating the cross-sectional view of a prior art EEFL. The prior art EEFL requires two driving circuits. For example, in the embodiment of FIG. 1, one driving circuit includes a pair of inner electrodes 11 and 12 stretching into the glass tube 15, and the other includes an outer electrode 13 surrounding the glass tube 15. The inner surface of the glass tube 15 is coated with fluorescent material and the inner space of the glass tube 15 is filled with gas 16. The gas 16 can be the mixture of some noble gases and Hg gas. When voltages are applied to the inner electrodes, the electrons are emitted from electrodes and bombard the Hg gas. Then, the excited Hg gas generates ultra-violet (UV) light when the Hg atoms transit from an excited state to a ground state. After the UV light then strikes the phosphor coated in the inner surface of the glass tube, visible light is hence emitted. Though EEFLs are proposed to solve the problems mentioned above, the working voltages of EEFLs are too high to result in a current leakage and the luminance of the lamp is reduced because the outer electrode 13 surrounding the lamp tube 15. Accordingly, further improvements in the back light module are still required for the industry.